“In the Arba`în of an-Nawawi, the thirteenth Hadith
talks about brotherhood. Imam an-Nawawi
says the ukhwa [ukhuwwa] in this hadith is that of
Bani Adam (i.e., of all humanity). Could you say more
on this hadith, and what other scholars have said on
its meaning and implications?”

According to the famous author of the Risala in Maliki fiqh, Imam Abi Zayd al-Qayrawani - as related by Imam al-Nawawi in his Minhaj of Hadith [2:210] - this Hadith is the last of the four Hadiths that constitute the famous "Sum of Good Adab" [Jima' Adab al-Khayr] (the first three being:
1. to speak little;
2. to mind one's own business;
3. not to be angry)
and in fact, according to many scholars then and now, this Hadith is one of the core principles of our religion and way of life
[Usul al-Din].

From the outset, it must be noted that all scholars are in agreement that "Iman" in the matn of this Hadith is to be qualified and that what is denied of Iman here is in fact the "complete iman" [kamal/tamm/nihayat/haqiqat al-Iman], not Iman or faith itself. Therefore, it must not become a question of a Muslim having Iman or not when he or she does not love his fellow "brother" (that is to say, it is not a question of Muslim vs. Kafir).

Imams al-Nawawi and Ibn al-'Imad (may Allah be pleased with them both!), for instance, were among our scholars who understood "brotherhood" in this Hadith (from the phrase: li-akhIhi [his brother] in the matn) to include all of humanity, i.e., the brotherhood of mankind (in the other ta'wil, brotherhood simply refers to Muslims). In fact, Imam Najm al-Din al-Tufi, the Hanbali mufassir, more plainly than any other medieval interpreter of this Hadith, used the expression "mahabbat al-insan" [the love for mankind]. [Tufi, Ta'yin, 125]. This, it turns out, is not astonishing, for his own Mujtahid Imam related a Hadith (reproduced below) that bears out the full relevance of our topic.

The implication of mahabba [love] with respect to brotherhood, whether taken in its universal sense (of mankind) or in its limited sense (of Muslims only), is that we wish for him what we wish for ourselves as well. So in the case of Muslims, for example, our wish is for him to remain in Islam while for the non-Muslim, on the other hand, our wish is for him to be in Islam; the motivation for this love, of course, should be none other than the sincere concern, ultimately, for well-being in the Hereafter. In fact, according to Imam al-Ghazali ( may Allah be pleased with him!), this principle is the acme of sukun, i.e., being at peace with the rest of creation, of which the sum is in fact, good manners or good Adab among people. And the peak of good Adab, says the Hujjat al-Islam, is that "you do not burden people according to your own pleasure, but burden yourselves according to their pleasures so long as they do not violate the Shari'a." [Ghazali, Ayyuha l-Walad, 131]

The most judicious explanation of this Hadith, indeed, was given by the collector, Imam al-Nawawi himself (and the same sharh was again related, but later ascribed by some to another Shafi'i jurist, the meticulous Ibn al-'Imad):
"It is better for that [saying of the Prophet, may Allah's blessings and peace be upon him!] to be interpreted in the sense of universal brotherhood, so that it includes the non-Muslim and the Muslim. Thus he wants for his non-Muslim brother what he would want for himself, that is [read: min li-l-bayan] his converting to Islam; just as he wants for his Muslim brother, his remaining in Islam. That is why it is recommended to supplicate for divine guidance [Hidaya] on behalf of the non-Muslim." [Nawawi, Sharh Arba'in, 123].

Let us close with another version of this Hadith, a most appropriate one for our discussion, and this is the version of the Mujtahid Imam Ahmad (as well as of Abu Ya'la, Ibn Hibban, and al-Rafi'i - the latter apparently through Ibn 'Umar; may Allah be well pleased with them all!):

[A man will not achieve true Iman until he wants for [other] men what he would want for himself of the good.]

Remarkably, this version has all three provisos that are indispensable for the teacher to explain and teach this Hadith: Haqiqa, Nas, and Khayr. Ma sha' Allahu kana! This shows why we should never limit ourselves (a condition our scholars call those of us who suffer from it as the "qasirin": people of limited insight) by reading a Hadith or the Qur'an literally [zahiran] or hurriedly [muruq al-sahm]
: for we will end up injuring ourselves!
May Allah keep us far from that malady and give us the patience to open our hearts and minds instead: Amin!